1. Field of the Invention
This invention relates to a power supply apparatus for supplying a power supply voltage to a microprocessor such as a CPU.
2. Description of the Related Art
A predetermined power supply voltage stabilized by a voltage regulator circuit (hereinafter simply referred to as a regulator circuit) is supplied to a microprocessor, such as a CPU, used in personal computers, workstations, game machines, and the like. A target power supply voltage to be supplied to a microprocessor is set according to a semiconductor manufacturing process or the like of the microprocessor. The power supply voltage of recent microprocessors manufactured using a low voltage process is about 1.2 V.
Currently, various types of microprocessors are supplied from different vendors. The microprocessors supplied from each vendor provide an instruction for the target power supply voltage to be supplied thereto to a regulator circuit by means of a unique method. In other words, the regulator circuit is designed to be capable of receiving the instruction regarding the target power supply voltage from the microprocessors. FIG. 6 is a block diagram illustrating an example of a conventional configuration of a microprocessor and a regulator circuit.
As shown in FIG. 6, a microprocessor 60 is connected to a regulator circuit 62 through, for example, a 5-bit parallel signal line 64. The microprocessor 60 sends a VID (Voltage ID) signal through the signal line 64 to provide an instruction for a target power supply voltage Vdd to be supplied thereto to the regulator circuit 62. The regulator circuit 62 generates the target power supply voltage Vdd designated by the microprocessor 60 and supplies the voltage to the microprocessor 60 through a power supply line 66. By employing such a configuration, when a user replaces the microprocessor 60 with another microprocessor 60 after a device having the microprocessor 60 and the regulator circuit 62 mounted thereon (hereinafter such a device is simply referred to as a set) is shipped, an optimal power supply voltage Vdd can be supplied to the replaced microprocessor 60.
However, with conventional technologies, when a set manufacturer selects a vendor of a microprocessor 10 to be used, the set manufacturer must select a regulator circuit 12 which is adaptable to the microprocessor 10 supplied from that vendor, and therefore design flexibility is limited. In addition, the resolution of the power supply voltage Vdd is limited by the number of bits of the VID signal sent to the regulator circuit 62 through the signal line 64, and this poses a problem in that the voltage cannot be finely adjusted.